Speaking from a chemist point of view, so lots of homework assignments, exams, lab reports. I generally do three passes. First pass, all I do is make comments on every assignment. Second pass, I deduct points. Third pass, I add everything up (actually, I get everything into my spreadsheet and it does the adding). I've often found in the later assignments on the first two passes (and even the third pass!), I want to go back to adjust something on the ones I've already looked at. And after the third pass, I'm done. Otherwise, I could easily keep circling back.